CLONE - If a section has multiple class periods on a given day, StudentSectionAttendanceEvent cannot represent a student being absent for only one of them, but not the other

Summary of Outcomes for Data Standard v3.3-b

• Problem Addressed: There is not a way to identify what class period a section attendance event applies to if there are multiple class periods referenced on the section definition.
  * High-Level Reasoning: Section attendance events should be granular enough to capture if a student missed one or more sections that may occur across multiple class periods on the same day.
  * Changes Made: Add an optional collection of ClassPeriod to StudentSectionAttendanceEvent.

Original Ticket Description:

Delaware has and extended studentSectionClassPeriodAttendanceEvent with ClassPeriodName added to the key in order to represent this data case.  I believe this changed with some of the 3.x changes.

I know I had some discussions around this with our initial implementation 2 years ago, but don't believe I ever entered a tracker ticket around it. 

We have a solution with our extension, but are upgrading from 3.1 (I hope) for the first time, so was reviewing our extensions to see what might have been put into core that could eliminate extensions.